Re: [PATCH v4 0/3] Compile-time stack frame pointer validation

From: Josh Poimboeuf
Date: Wed May 20 2015 - 10:14:20 EST

On Wed, May 20, 2015 at 12:33:39PM +0200, Ingo Molnar wrote:
>
> * Josh Poimboeuf <jpoimboe@xxxxxxxxxx> wrote:
>
> > In discussions around the live kernel patching consistency model RFC
> > [1], Peter and Ingo correctly pointed out that stack traces aren't
> > reliable. And as Ingo said, there's no "strong force" which ensures we
> > can rely on them.
> >
> > So I've been thinking about how to fix that. My goal is to eventually
> > make stack traces reliable. Or at the very least, to be able to detect
> > at runtime when a given stack trace *might* be unreliable. But improved
> > stack traces would broadly benefit the entire kernel, regardless of the
> > outcome of the live kernel patching consistency model discussions.
> >
> > This patch set is just the first in a series of proposed stack trace
> > reliability improvements. Future proposals will include runtime stack
> > reliability checking, as well as compile-time and runtime DWARF
> > validations.
> >
> > As far as I can tell, there are two main obstacles which prevent frame
> > pointer based stack traces from being reliable:
> >
> > 1) Missing frame pointer logic: currently, most assembly functions don't
> > set up the frame pointer.
>
> Could you please paste here the output of what the new checks print
> for x86/64 defconfig?

Here are all 89 warnings from defconfig:

arch/x86/ia32/ia32entry.o: ia32_sysenter_target() is missing frame pointer logic. Please use FUNC_ENTER.
arch/x86/ia32/ia32entry.o: return instruction outside of a function at .entry.text+0x52e. Please use FUNC_ENTER.
arch/x86/kernel/entry_64.o: return instruction outside of a function at .entry.text+0x359. Please use FUNC_ENTER.
arch/x86/kernel/entry_64.o: return instruction outside of a function at .entry.text+0x19be. Please use FUNC_ENTER.
arch/x86/kernel/entry_64.o: return instruction outside of a function at .entry.text+0x19e5. Please use FUNC_ENTER.
arch/x86/kernel/entry_64.o: return instruction outside of a function at .entry.text+0x1c21. Please use FUNC_ENTER.
arch/x86/kernel/entry_64.o: return instruction outside of a function at .entry.text+0x1ceb. Please use FUNC_ENTER.
arch/x86/kernel/acpi/wakeup_64.o: wakeup_long64() is missing frame pointer logic. Please use FUNC_ENTER.
arch/x86/kernel/acpi/wakeup_64.o: do_suspend_lowlevel() is missing frame pointer logic. Please use FUNC_ENTER.
arch/x86/platform/efi/efi_stub_64.o: efi_call() is missing frame pointer logic. Please use FUNC_ENTER.
arch/x86/kernel/relocate_kernel_64.o: return instruction outside of a function at .text+0x6b. Please use FUNC_ENTER.
arch/x86/kernel/relocate_kernel_64.o: return instruction outside of a function at .text+0xc7. Please use FUNC_ENTER.
arch/x86/kernel/relocate_kernel_64.o: return instruction outside of a function at .text+0x110. Please use FUNC_ENTER.
arch/x86/kernel/relocate_kernel_64.o: return instruction outside of a function at .text+0x145. Please use FUNC_ENTER.
arch/x86/kernel/relocate_kernel_64.o: return instruction outside of a function at .text+0x1c4. Please use FUNC_ENTER.
arch/x86/realmode/rm/trampoline_64.o: return instruction outside of a function at .text+0x170. Please use FUNC_ENTER.
arch/x86/realmode/rm/trampoline_64.o: return instruction outside of a function at .text+0x176. Please use FUNC_ENTER.
arch/x86/kernel/head_64.o: return instruction outside of a function at .head.text+0x1a2. Please use FUNC_ENTER.
arch/x86/kernel/head_64.o: start_cpu0() is missing frame pointer logic. Please use FUNC_ENTER.
arch/x86/kernel/head_64.o: early_idt_handler() is missing frame pointer logic. Please use FUNC_ENTER.
arch/x86/realmode/rm/reboot.o: return instruction outside of a function at .text+0x2a. Please use FUNC_ENTER.
arch/x86/realmode/rm/copy.o: memcpy() is missing frame pointer logic. Please use FUNC_ENTER.
arch/x86/realmode/rm/copy.o: memset() is missing frame pointer logic. Please use FUNC_ENTER.
arch/x86/realmode/rm/copy.o: copy_from_fs() is missing frame pointer logic. Please use FUNC_ENTER.
arch/x86/realmode/rm/copy.o: copy_to_fs() is missing frame pointer logic. Please use FUNC_ENTER.
arch/x86/realmode/rm/bioscall.o: intcall() is missing frame pointer logic. Please use FUNC_ENTER.
arch/x86/vdso/vdso32/int80.o: __kernel_sigreturn() is missing frame pointer logic. Please use FUNC_ENTER.
arch/x86/vdso/vdso32/int80.o: __kernel_rt_sigreturn() is missing frame pointer logic. Please use FUNC_ENTER.
arch/x86/vdso/vdso32/int80.o: __kernel_vsyscall() is missing frame pointer logic. Please use FUNC_ENTER.
arch/x86/vdso/vdso32/syscall.o: __kernel_sigreturn() is missing frame pointer logic. Please use FUNC_ENTER.
arch/x86/vdso/vdso32/syscall.o: __kernel_rt_sigreturn() is missing frame pointer logic. Please use FUNC_ENTER.
arch/x86/vdso/vdso32/syscall.o: __kernel_vsyscall() is missing frame pointer logic. Please use FUNC_ENTER.
arch/x86/vdso/vdso32/sysenter.o: __kernel_sigreturn() is missing frame pointer logic. Please use FUNC_ENTER.
arch/x86/vdso/vdso32/sysenter.o: __kernel_rt_sigreturn() is missing frame pointer logic. Please use FUNC_ENTER.
arch/x86/power/hibernate_asm_64.o: return instruction outside of a function at .text+0x69. Please use FUNC_ENTER.
arch/x86/power/hibernate_asm_64.o: return instruction outside of a function at .text+0x16d. Please use FUNC_ENTER.
arch/x86/lib/msr-reg.o: rdmsr_safe_regs() is missing frame pointer logic. Please use FUNC_ENTER.
arch/x86/lib/msr-reg.o: wrmsr_safe_regs() is missing frame pointer logic. Please use FUNC_ENTER.
arch/x86/lib/iomap_copy_64.o: __iowrite32_copy() is missing frame pointer logic. Please use FUNC_ENTER.
arch/x86/lib/clear_page_64.o: clear_page() is missing frame pointer logic. Please use FUNC_ENTER.
arch/x86/lib/clear_page_64.o: clear_page_orig() is missing frame pointer logic. Please use FUNC_ENTER.
arch/x86/lib/clear_page_64.o: clear_page_c_e() is missing frame pointer logic. Please use FUNC_ENTER.
arch/x86/lib/cmpxchg16b_emu.o: this_cpu_cmpxchg16b_emu() is missing frame pointer logic. Please use FUNC_ENTER.
arch/x86/lib/copy_page_64.o: copy_page() is missing frame pointer logic. Please use FUNC_ENTER.
arch/x86/lib/copy_page_64.o: copy_page_regs() is missing frame pointer logic. Please use FUNC_ENTER.
arch/x86/lib/copy_user_64.o: _copy_to_user() is missing frame pointer logic. Please use FUNC_ENTER.
arch/x86/lib/copy_user_64.o: _copy_from_user() is missing frame pointer logic. Please use FUNC_ENTER.
arch/x86/lib/copy_user_64.o: copy_user_generic_unrolled() is missing frame pointer logic. Please use FUNC_ENTER.
arch/x86/lib/copy_user_64.o: copy_user_generic_string() is missing frame pointer logic. Please use FUNC_ENTER.
arch/x86/lib/copy_user_64.o: copy_user_enhanced_fast_string() is missing frame pointer logic. Please use FUNC_ENTER.
arch/x86/lib/copy_user_64.o: __copy_user_nocache() is missing frame pointer logic. Please use FUNC_ENTER.
arch/x86/lib/copy_user_64.o: bad_from_user() is missing frame pointer logic. Please use FUNC_ENTER.
arch/x86/lib/csum-copy_64.o: csum_partial_copy_generic() is missing frame pointer logic. Please use FUNC_ENTER.
arch/x86/lib/getuser.o: __get_user_1() is missing frame pointer logic. Please use FUNC_ENTER.
arch/x86/lib/getuser.o: __get_user_2() is missing frame pointer logic. Please use FUNC_ENTER.
arch/x86/lib/getuser.o: __get_user_4() is missing frame pointer logic. Please use FUNC_ENTER.
arch/x86/lib/getuser.o: __get_user_8() is missing frame pointer logic. Please use FUNC_ENTER.
arch/x86/lib/getuser.o: return instruction outside of a function at .text+0xc5. Please use FUNC_ENTER.
arch/x86/lib/memcpy_64.o: memcpy() is missing frame pointer logic. Please use FUNC_ENTER.
arch/x86/lib/memcpy_64.o: __memcpy() is missing frame pointer logic. Please use FUNC_ENTER.
arch/x86/lib/memcpy_64.o: memcpy_erms() is missing frame pointer logic. Please use FUNC_ENTER.
arch/x86/lib/memcpy_64.o: memcpy_orig() is missing frame pointer logic. Please use FUNC_ENTER.
arch/x86/lib/memmove_64.o: memmove() is missing frame pointer logic. Please use FUNC_ENTER.
arch/x86/lib/memmove_64.o: __memmove() is missing frame pointer logic. Please use FUNC_ENTER.
arch/x86/lib/memmove_64.o: return instruction outside of a function at .altinstr_replacement+0x5. Please use FUNC_ENTER.
arch/x86/lib/memset_64.o: memset() is missing frame pointer logic. Please use FUNC_ENTER.
arch/x86/lib/memset_64.o: __memset() is missing frame pointer logic. Please use FUNC_ENTER.
arch/x86/lib/memset_64.o: memset_erms() is missing frame pointer logic. Please use FUNC_ENTER.
arch/x86/lib/memset_64.o: memset_orig() is missing frame pointer logic. Please use FUNC_ENTER.
arch/x86/lib/putuser.o: __put_user_1() is missing frame pointer logic. Please use FUNC_ENTER.
arch/x86/lib/putuser.o: __put_user_2() is missing frame pointer logic. Please use FUNC_ENTER.
arch/x86/lib/putuser.o: __put_user_4() is missing frame pointer logic. Please use FUNC_ENTER.
arch/x86/lib/putuser.o: __put_user_8() is missing frame pointer logic. Please use FUNC_ENTER.
arch/x86/lib/putuser.o: return instruction outside of a function at .text+0xc1. Please use FUNC_ENTER.
arch/x86/lib/rwsem.o: call_rwsem_down_read_failed() is missing frame pointer logic. Please use FUNC_ENTER.
arch/x86/lib/rwsem.o: call_rwsem_down_write_failed() is missing frame pointer logic. Please use FUNC_ENTER.
arch/x86/lib/rwsem.o: call_rwsem_wake() is missing frame pointer logic. Please use FUNC_ENTER.
arch/x86/lib/rwsem.o: call_rwsem_downgrade_wake() is missing frame pointer logic. Please use FUNC_ENTER.
arch/x86/boot/bioscall.o: intcall() is missing frame pointer logic. Please use FUNC_ENTER.
arch/x86/boot/copy.o: memcpy() is missing frame pointer logic. Please use FUNC_ENTER.
arch/x86/boot/copy.o: memset() is missing frame pointer logic. Please use FUNC_ENTER.
arch/x86/boot/copy.o: copy_from_fs() is missing frame pointer logic. Please use FUNC_ENTER.
arch/x86/boot/copy.o: copy_to_fs() is missing frame pointer logic. Please use FUNC_ENTER.
arch/x86/boot/pmjump.o: protected_mode_jump() is missing frame pointer logic. Please use FUNC_ENTER.
arch/x86/boot/pmjump.o: in_pm32() is missing frame pointer logic. Please use FUNC_ENTER.
arch/x86/boot/compressed/head_64.o: return instruction outside of a function at .text+0x16e. Please use FUNC_ENTER.
arch/x86/boot/compressed/head_64.o: return instruction outside of a function at .text+0x172. Please use FUNC_ENTER.
arch/x86/boot/compressed/head_64.o: startup_32() is missing frame pointer logic. Please use FUNC_ENTER.
arch/x86/boot/header.o: die() is missing frame pointer logic. Please use FUNC_ENTER.

> > As a first step, all reported non-compliances result in warnings.
> > Right now I'm seeing 200+ warnings. Once we get them all cleaned
> > up, we can change the warnings to build errors so the asm code can
> > stay clean.
>
> That's quite a bit ...

Yeah, a Fedora-based config has over 200 warnings. Most of the
differences between the above 89 warnings for defconfig and the 200+ for
a Fedora config seem to be caused by xen, crypto and bpf.

--
Josh
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